feat: Go backend, enhanced search, new widgets, Docker deploy

Major changes:
- Add Go backend (backend/) with microservices architecture
- Enhanced master-agents-svc: reranker, content-classifier, stealth-crawler,
  proxy-manager, media-search, fastClassifier, language detection
- New web-svc widgets: KnowledgeCard, ProductCard, ProfileCard, VideoCard,
  UnifiedCard, CardGallery, InlineImageGallery, SourcesPanel, RelatedQuestions
- Improved discover-svc with discover-db integration
- Docker deployment improvements (Caddyfile, vendor.sh, BUILD.md)
- Library-svc: project_id schema migration
- Remove deprecated finance-svc and travel-svc
- Localization improvements across services

Made-with: Cursor

backend/pkg/middleware/ratelimit.go

@@ -0,0 +1,106 @@
+package middleware
+
+import (
+	"sync"
+	"time"
+
+	"github.com/gofiber/fiber/v2"
+)
+
+type RateLimitConfig struct {
+	Max        int
+	WindowSecs int
+	KeyFunc    func(*fiber.Ctx) string
+}
+
+type rateLimiter struct {
+	requests map[string][]time.Time
+	mu       sync.RWMutex
+	max      int
+	window   time.Duration
+}
+
+func newRateLimiter(max int, windowSecs int) *rateLimiter {
+	rl := &rateLimiter{
+		requests: make(map[string][]time.Time),
+		max:      max,
+		window:   time.Duration(windowSecs) * time.Second,
+	}
+
+	go rl.cleanup()
+	return rl
+}
+
+func (rl *rateLimiter) cleanup() {
+	ticker := time.NewTicker(time.Minute)
+	for range ticker.C {
+		rl.mu.Lock()
+		now := time.Now()
+		for key, times := range rl.requests {
+			var valid []time.Time
+			for _, t := range times {
+				if now.Sub(t) < rl.window {
+					valid = append(valid, t)
+				}
+			}
+			if len(valid) == 0 {
+				delete(rl.requests, key)
+			} else {
+				rl.requests[key] = valid
+			}
+		}
+		rl.mu.Unlock()
+	}
+}
+
+func (rl *rateLimiter) allow(key string) bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+
+	now := time.Now()
+	windowStart := now.Add(-rl.window)
+
+	times := rl.requests[key]
+	var valid []time.Time
+	for _, t := range times {
+		if t.After(windowStart) {
+			valid = append(valid, t)
+		}
+	}
+
+	if len(valid) >= rl.max {
+		rl.requests[key] = valid
+		return false
+	}
+
+	rl.requests[key] = append(valid, now)
+	return true
+}
+
+func RateLimit(config RateLimitConfig) fiber.Handler {
+	if config.Max == 0 {
+		config.Max = 100
+	}
+	if config.WindowSecs == 0 {
+		config.WindowSecs = 60
+	}
+	if config.KeyFunc == nil {
+		config.KeyFunc = func(c *fiber.Ctx) string {
+			return c.IP()
+		}
+	}
+
+	limiter := newRateLimiter(config.Max, config.WindowSecs)
+
+	return func(c *fiber.Ctx) error {
+		key := config.KeyFunc(c)
+
+		if !limiter.allow(key) {
+			return c.Status(429).JSON(fiber.Map{
+				"error": "Too many requests",
+			})
+		}
+
+		return c.Next()
+	}
+}